Phycocolloids are natural gums produced by and extracted from marine algae. The three principal types of commercially valuable phycocolloids are agar, carrageenan and alginate. By far the seaweeds which have been successfully cultivated include red algae (Porphyra, Gracilaria, Gelidium, Euchema), green algae (Ulva) and brown algae (Laminaria, Undaria). The global cultivation areas for seaweeds are 3 million mu, with annual production more than 6.35 million tons (wet weight), most of which were utilized to extract the phycocolloids, except a small amount as nutrition food. In recent years, due to quickly-increased demands to the phycocolloids production and quality improvement, the genetic transformation techniques were introduced to the seaweed research fields, with purpose to directionally improve the seaweeds traits, also the great potential for expression of high-value products has been suggested.
To date, most of the well-developed techniques to generate transgenic plant are employed for high plants, which include:
1. Transformation methods: Agrobactarium Ti plasmid-mediated transformation, electroporation to protoplast, and Biolistics to explant; 2. Vector element: high plant-derived promoters (i.e. CaMV35S) have been used widely to drive the expression of foreign genes; 3. Transformation recipient and plant regeneration: to take advantage of the totipotency, that is to regenerate protoplast, or induce the callus formation and further differentiation to regenerate new plant; 4. Selectable marker: Npt II gene was used most widely as selectable marker that, transgenic plant could be obtained by selection with kanamycin or neomycin.
Seaweeds are low plants that live in marine environment, they are of significant difference which including: 1. Transformation methods: no well-developed methods like Agrobactarium Ti plasmid-mediated transformation to high plant; 2. Vector element: no seaweed-derived promoter has been obtained; 3. Transformation recipient and plant regeneration: there's significant difference on research extent between species, protoplast regeneration was easy in some genus like Porphyra, but very hard in others like Laminaria and Undaria, as well as low efficiency for callus induction; 4. Selectable marker: sensitive antibiotics types and sensitivity extent maybe different between seaweed and high plant.
By far most researches on seaweed transformation have referred the techniques applied in high plant, those are to transfer the seaweed explants or protoplast as transformation recipient. Only transient expression has been obtained, and no expression was detected in regenerated plant, even the transient transformation efficiency is low since only high plant-derived promoters (e.g. CaMV35S) are available; no sensitivity test on seaweed to antibiotics have been done yet.